Chain length, determination

Finally, ion chromatography can be used to determine the a-sulfo fatty acid esters. The chromatographic column is a nonpolar poly sty rene/divinylbenzene column and the ion pair reagent is 0.005 M ammonia. In order to reduce the elution time, acetonitrile is added as a modifier with increasing concentration. This gradient technique makes it possible to separate simultaneously ester sulfonates and disalts by chain length. Determination is achieved by standards with defined chain length [107]. 

Notably, natural variation in the type III PKS active site cavity, like that observed in Ipomoea and Petunia, does not result in functionally impaired enzymes, but in fact, generates catalytically active enzymes that display both altered substrate and product specificities. Sequential increases in the side chain volume of position 256 in alfalfa CHS2 result in decreases in polyketide chain length and predictable shifts in the ratio of tetraketide to triketide reaction products.32 These results functionally link the volume of the elongation/cyclization lobe in type III PKS to chain length determination. 

JEZ, J.M., BOWMAN, M.E., NOEL, J.P., Structure-guided programming of polyketide chain-length determination in chalcone synthase, Biochemistry, 2001, 40, (in press). 

Kahrel Y, Takahashi S, Yamashita S et al (2006) Manipulation of prenyl chain length determination mechanism of ci s-prenyltransferases. FEES J 273 647-657... 

If short-chain alkyltrimethylammonium ions, R(CH3)3N", are used as the surfactant, the alkyl chain length determines whether micro- or mesoporous materials are formed. For alkyl chain lengths of Ce or shorter, microporous zeolites such as ZSM-5 are formed but for longer chains, mesoporous materials are isolated. 

Smith, S. 1980. Mechanism of chain length determination in biosynthesis of milk fatty acids. J. Dairy Sci. 63, 337-352. 

Delgado, M., Mouslim, C., Groisman, E. The PmrA/PmrB and RcsC/YojN/RcsB systems control expression of the Salmonella O-antigen chain length determinant. Mol Microbiol 60 (2006) 39-50. 

Thus, authors often apply the term visible PolyPs when discussing the results obtained by this method (Loureiro-Dias and Santos, 1990). It can be considered that the most reliable approach is the combination of PolyP chain length determination by NMR spectroscopy with the method of chemical extraction from cells and their quantitative analysis. 

Chain length determination seems to use a counting mecha-lusm as in the case of the Type 2 actinorhodin PKS. Incubation of various acyl CoA starter units with malonyl CoA with MSAS in the absence of NADPH and acetyl CoA resulted in two chain extensions to produce the corresponding substituted TALs. 

An example is the use of pre-gastric lipases for the production of Italian cheese types. In these cheeses the entire stomach of calves is dried and used. This results in a characteristic piquant flavour. The substrate specificity of the lipases, in terms of affinity for certain fatty acid chain lengths, determines the quality and the flavour of the final lipolyses product. 

Figure 3-8. Proposed mechanism of the chain-length determination of the wild-type and variant heptaprenyl diphosphate synthases based on the pocket mechanism. A, Wild-type enzyme ...

K. Hirooka, S. Ohnuma, A. Koike-Take-shita, T. Koyama, T. Nishino, Mechanism of product chain length determination for heptaprenyl diphosphate synthase from Bacillus stearothermophilus, Eur. J. Biochem. 2000, 267(14), 4520-4528. 

H. Hemmi, T. Nishino, The role of histidine-114 of Sulfolobus acidocaldarius gera-nylgeranyl diphosphate synthase in chain-length determination, FEBS Lett. 2000, 481(1), 68-72. 

The least sophisticated but most convenient technique illustrating polymer fractionation is fractional precipitation, which is dependent on the slight change in the solubility parameter with molecular weight. Thus, when a small amount of miscible nonsolvent is added to a polymer solution at a constant temperature, the product with the highest molecular weight precipitates. This procedure may be repeated after the precipitate is removed. These fractions may also be redissolved and fractionally precipitated. The shape of the distribution curve is then constructed from the fractional amount of each sample after chain length determination. 

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